Diabetes is a complex disorder with three main subtypes, type I, type II and monogenic. Type I is an autoimmune disorder characterized by loss of the insulin secreting beta cell. Type II is metabolic disorder characterized by poor insulin responsiveness and eventual beta cell exhaustion and loss. Monogenic forms are caused by mutations in a number of genes that are generally important in beta cell development and/or function. This proposal will focus on the study on HNF1A, a transcription factor that when mutated leads to the most common cause on monogenic diabetes. In addition, HNF1A has been linked to both type I and type II diabetes in GWAS studies. Mouse models of HNF1A deficiency are available, but unfortunately do not appropriately mimic the human disease. Therefore, use of a human model system is important. We will use the human pluripotent stem cell model to study the role of HNF1A in both endocrine cell development and function, utilizing CRISPR-Cas9 based genome engineering to generate isogenic mutant lines. Robust in vitro differentiation protocols exist and will be used to generate beta cells in the human stem cell model. In preliminary studies, we have uncovered human specific HNF1A targets that have been validated in a dataset from an individual with monogenic diabetes due to a HNF1A mutation. We have also discovered phenotypes in metabolic functions in HNF1A mutant stem cell derived beta cells, offering a potential link between the association of HNF1A with type II and possibly type I diabetes. Lastly, one of the human specific targets of HNF1A is a long non-coding RNA that when deleted in stem cells, mimics some of the metabolic phenotypes seen in the HNF1A mutants. These studies will help define the developmental and functional requirements of HNF1A in pancreatic endocrine cells and have the potential to directly impact the treatment of not only rare monogenic forms of diabetes but also type I and type II diabetes.